The goal of this research is to develop "smart" radiolabels that produce ? ray signal only when an exciter and emitter are in close proximity of each other. This technology would allow imaging of molecular interactions and close co-localization through deep tissue. This technology would also dramatically increase the specificity of imaging and could provide a general solution to the problem of imaging gene expression at the mRNA level. The experimental goal is to test these novel radiolabels in vitro. The first step is to synthesize exciters and emitters conjugated to biotin and avidin in order to test the interaction in a biological context. Then taking advantage of the strength of the avidin-biotin interaction, exciters and emitters would be allowed interact and the total ? ray yield will be measured. The interaction will be tested using four different geometries and configurations in order to experimentally establish parameters for the most efficient ? ray yield. For a control, exciters and emitters will be suspended in solution and the background ? ray yield will be measured.